Modern motor vehicles have a large number of electrical or electronic switching devices which are actuated by a user for controlling a desired function. For example, pressure switches, toggle switches or the like on the dashboard of the motor vehicle as well as on steering column or steering wheel switches are known, for example for controlling a direction indicator or a windscreen washer system. If such a switching device is actuated, usually an electrical circuit is closed or a corresponding control signal is forwarded to a corresponding control device of the motor vehicle, which in turn controls the actual desired function.
In the process there frequently arises the problem that the user or his fingertip is electrostatically charged and this electrical charge is transferred to the switching device upon touching the latter. In the process there can be an electrostatic discharge (ESD for short). Even with an electrically insulating material, for example, a plastic surface of the electrical switching device, a spark can arise, which penetrates through the material and causes in the switching device a short creating a high electrical current pulse. Particularly in the case of delicate electrical or electronic switching devices, this can lead to damage.
To protect electrical switching devices, various solutions are known. DE 10 2004 027 278 A1 describes a protective circuit with a semiconductor substrate, active components such as, for example, transistors being contained in the semiconductor substrate. DE 10 2005 027 368 A1 discloses a protective semiconductor structure for an electrostatic discharge with two bipolar transistors between which the electrostatic charge is conducted back and forth in order to reduce it. Lastly, from DE 10 2004 052 093 A1 is known a circuit assembly which consists of two sections, each with its own operating voltage and a transistor. These solutions are, however, disadvantageous insofar as they require considerable expenditure on circuitry and introduction of the electrostatic charge into the circuit itself is likewise not reliably guaranteed.
Furthermore it is known from practical experience that an anti-ESD device can be formed by a labyrinth in the gap region between an actuating element and a housing of switching devices, the labyrinth being intended to prevent penetration of a spark into the interior of the switching device.